Packaging in stretched film



April 417, 1951 H, J. OSTERHOF 2,549,122

PACKAGING IN STRETCHED FILM Filed April 3, 1948 INVENTOR. HAROLD J.OSTERHOF ATTORNEY Patented Apr. 17, 1951 Harold Judson Osterhof, Akron,

Ohio, assignor to Wingfoot Corporation, Akron, Ohio, a .corporation ofDelaware Application April 3, 1948, Serial No. 18,831

5 Claims.

This invention relates to the packaging of articles in stretched lilm.It includes the process of packaging andapparatus for carrying out theprocess.

The film used for packaging is a stretched plastic iilm which is ofunstable equilibrium and shrinks when heated. There are various plasticlms .on the market which might be stretched and used for the purpose.Such lms include lms of rubber hydrochloride (Pliolm), vinyl chloridepolymer and copolymers, vinylidene chloride copolymers, polyethylene,mixtures of (1) vinyl polymer and (2) copolymer of butadiene andacrylonitrile, etc. A preferred film for the purpose is rubberhydrochloride lm.

By stretching, the area of the lm is increased so that a given weight offilm gives greater coverage. The cost of the film required for packaginganarticle may thus be decreased. Thus, rubber hydrochloride film may bestretched to several times its original area; e. g., from less thanfourto more than thirty-fold. It may be stretched only laterally; inwhich case, on heating, it shrinks laterally. If stretchedlongitudinally, it shrinks longitudinally when heated, The film may bestretched in both directionssuocessively or simultaneously. If thestretching in both directions is not simultaneous, the tendency is forthe lm to shrink most in the direction in which it was last stretched.

The tendency of the film to shrink on heating has certain advantages.`Thus, by enclosing an article in the stretched lm and then heating thefilm, the Wrapper may be shrunk to form a snug fit around the article.chloride iilm appears to be unique in retaining the tendency to shrinkfor a considerable period after being heated even though, in themeantime, the nlm be cooled to room temperature'. Thus, in a packagingoperation in which rubber hydrochloride film is employed, if the lm hasbeen heated at any stage of the operation, it may be kept under tensionvuntil cooled land will 'then i shrink when the tension is released.Other lms shrink only While heated.

The conditions required for most perfect preservation of articlesvaries. For instance, fruits and vegetables immediately after pickingconl tinue to breathe, and a lm permeable to the exhaled gases may givebetter preservation than a lm which is impermeable to the transmissionof such gases. i Furthermore, `although generally it may be desirable touse a moisture-tight film to prevent loss of moisture from the articlebeing packaged (or to prevent the absorption of mois- Rubber hydro- 2 iture by the article being packaged), some permeability to moisture mayat times be desirable. Thus, a thin film which is more permeable tomoisture, etc., may be preferred for wrapping certain articles than athicker Iilm which is more impervious. The lm may be compounded withspecific plasticizers or softeners, etc., to further control thepermeability l,of the `iilm to moisture and gases. Thus the compositionVand thickness of the film may be selected with a view vto maintainingthe article in an atmosphere best suited for its preservation. i

The apparatus disclosed is designed particularly for use on film whichhas been simultaneously or consecutively stretched in both directions(referred to hereinafter as double-stretched iilm), the amount ofstretch in each direction being sufficient to at least double the areaof the film. The invention Will be more particularly described inconnection `vvith the packaging'of loaves of bread in rubberhydrochloride film plasticized with from 5 to l5 per cent 0f butylstearate, dibutyl phthalate, dibutyl sebacate, etc., either used singlyor in admixture with each other. The lm is prepared from thiscomposition by iirst casting from a solution, evaporating the solvent,and then heating land stretching the hlm thus obtained. Cast film (afterevaporation of the solvent) may, for example, be up to about .0014.-inch thick, more or less. On stretching, the lm is stretched at leasttwo-fold in each direction so that the resultant nlm used in thepackaging operation is thus in the range of 0.0001 to 0.0004 inch thick.

The loaves of bread are fresh loaves, and it is important that thewrapper be relatively moisture tight although some loss of moisture isdesirable. The lm may advantageously include vsome fungicide to preventthe growth of mold. Bread packaged in such film may be preserved arelatively long time in a substantially fresh condition. i

It is to be understood that although the invention is described inconnection with the Wrapping of bread, with slight adjustment theequipment may be used for the packaging of other f articles by the samegeneral process as herein disclosed.

In the accompanying drawings:

Fig. 1 is an elevation (more or less diagrammatic) of equipment whichmay be used and shows such equipment in use;

, Fig. 2 isan enlarged section onthe line-'2--2 of Fis, 1;

' tions 9 of the rollers 8.

Figs. 4 and 5 are details of the cut-olf device at different stages ofthe cutting-off operation.

In wrapping the loaves of bread or other articles, two continuous,narrow strips of the stretched film are employed, and these are formedinto a tube around the articles. The cut-off device -may be used with atube formed in any manner, such as a tube formed from a single sheet.The articles may be fed into the tube in any practical way.

In the drawing the thin double-stretched rubber hydrochloride lms I and2 are supplied from the rolls 3 and 4. The loaves 5 are fed between thelms manually or by suitable automatic means.

The belt 1 conveys the loaves between suitable operating means to thecut-01T. There are openings in the middle of the belt atV spacedintervals to receive the loaves of bread, and thus the loaves areconveyed to the cut-01T, supported by the ,lower film. Figs. 2 and 3show the belt 'I support the loaves at intervals as they yarev fed tothe cut-off. Fig. 2 is a section through an unperforated. width of thebelt; whereas Fig. 3 shows the loaf 5 supported in one of the openingsin the belt. The loaf is supported below by the film 2 and is coveredabove by the film I. To prevent the weight of the loaf from placing toogreat a strainon the film 2, a separate, narrow belt may be provided tobe supported by the por- The two films are sealed together near theiredges. This is done by the vapplication of heat and pressure. Ordinaryheat-sealing means will 'not be satisfactory because of the tendency ofthe film to shrink when heated. Shrinking is prevented by holding thefilm in place while heating. This is done by the belts I2, I2 which aresupported by the pulleys I3. The pulleys, in turn, are supported insuitable bearings held by the frame I6, This frame is adapted to belifted from and lowered onto' the conveyer belt. Ihe frame is weightedor otherwise constructed in such a way as to apply pressure through thebelts I2 to the films so as to prevent shrinkage when heat is applied attheir edges. The belts are located closely adjacent to the loaves ofbread so that the films are sealed closely adjacent the loaves.

The heat-sealing rollers I8 which unite the edges of the lm are locatedoutside of the belts. Thus, any shinkage which occurs does not affectthe film between the two belts I2. As shown in 3, the rollers I8comprise the two parts |811,` and I8b, which are in intimate contact.The wide portion I8a, which is nearest the loaf of bread, is constructedof a material which is an inferior heat conductor, such as the fibrous,noninflammable mineral composition known as Transite, manufactured bythe Johns-Manville Corporation, or the poly-tetrafluorethylene known asTeon and made by Du Pont, or Silastic 4 support is lowered so that therollers I8 press down on the films. The thin disk I8b is` heatedeelctrically or by other suitable means,and it is heated to atemperature of about 300 F. or higher and quickly melts its way throughthe two layers of doublestretched rubber hydrochloride film. `'The disk13a is heated by' thermal conduction from the disk ISb. It is'at a lowertemperature than the disk I3b and is not hot enough to melt its waythrough the films but is sufciently warm, for example, at a temperatureof about 230 F. to 300 F. so that it seals the two films of rubberhydrochloride together. The temperature of the disk Ia will not beuniform, but the portion adjacent the disk Ib will be hotter than thatlocated farther from the disk ISb. The temperature will be so adjustedthat the disk Ib melts through the lms whilethey are simultaneouslyrubber, a product ofthe Dow-Corning Corporabeing sealed together by thedisk IBa. The disk I8b may be ofV slightly greater diameter than thedisk Ia although this is not necessary.

After passing under the rollers I8`where th films are trimmed and sealedtogether, the film will tend to contract around the loaves. Whilegripped between the belts I2 and the conveyer belt l, they cannotshrink, but they do contract as soon as they pass out from under theends of the belts I2. I Y

The cut-ofi' operates intermittently. The movement of the belt is madeintermittent because the film must be held motionless whenV the cut-offis in operation. The cut-off comprises the support 3B (which is raisedand lowered as indicated in Fig. l) and the air cylinder 3| whichoperates the plunger 32 (Figs. 4 and 5) Mounted on the plunger are meansfor holding the film and other means for cutting it off and sealing it.The'holding means is the channel 33. The cut-off vand sealing unit iswithin this channel and comprises the hot plate 34 which is locatedbetween the thicker plates 35 which are rather poor conductors of heatand are advantageously made of Transite, Teflon, Silastic rubber or thelike. The elements of this cut-off and heat-sealing equipment nd theircounterpart in the equipment just described which is used for sealingthe films longitudinally. Y i y When the plunger 32 descends, the edgesof the channel 33 press the two films tightly against the support 30along two parallel'lines." [The pressure on the channel 33 is exertedthrough the spring V3l. As the plunger 32 continues to descend, the lmis contacted by the cut-ofi' and heat-sealing element which is fixeddirectly to the plunger. The lm is cut olf by the hot plate 3,4 midwaybetween theV two plates of the Ychannel 33. The sealing units 35 whichflank the hot plate sealv the lms on opposite sides of the cut-oil".Thus, as the film between each two loaves is severed, the Vfilms onopposite sides of the cutoil` ares'ealed. These two lateral seals andthe longitudinal seals made by the rollers I8 completely enclose eachloaf. n j "f As will be seen from an inspection of l'ig.` 1, as' thechannel 33 presses down on the film between the' adjacent loaves, ittendsV tobring the loaves together. The cut-off is thus not effected incontact with the loaf but is spaced a short distance from it. As thelongitudinaltension on the lm is released by raising the channel 33 andlowering the support 3U, the film, heated during the cut-off and sealingoperation," shrinks tightlv'to.- ward thee'nds of the loaves.Similarlythe filmY shrinks laterally around the circumference of! eachloaf yas it is released from the grip of the belts I2. The film thusshrinks toward the loaf on all sides and forms a snug enclosure aroundit.

Fig. l shows the packaged loaves delivered from the cut-off onto thebelt 40. If for any reason the wrapper is somewhat loose on the articlesafter the cut-ofi, the conveyer t0 may take them through an oven orunder radiant heat or otherwise subject them to sufcient heat to causethe enclosing films to fit snugly around the loaves.

Other modifications in the equipment shown are possible withoutdeparting from the appended claims which define the invention. rIihus,the shape of the article is not an essential feature of the invention.If round articles-such as oranges, grapefruit, and the like-are beingpackaged, they need not lit down through openings in the belt, but theopenings may be of less diameter than the fruit so that the fruit issupported at the edge of each opening.. Instead of providing openings inthe belt, other spacing means may be utilized. Instead of uniting thelms at their edges and then cutting them off, oblong or circular orother suitable means may be provided at the cut-off for uniting andcutting away excess film from all sides of the articles simultaneously.Thus, if oranges are being packaged, circular means may come down overeach orange to hold the film and then cut off and unite the two films.The cut-ofi blade may operate separately from the sealing bladesalthough unitary means for cutting off and sealing will ordinarily bepreferred. The articles being packaged may. be conveyed to the cut-offseveral abreast if desired. The two films need not be of the same gaugeand may be of different composition. Instead of separate lms, a singlefilm may be used and folded to cover the tops and bottoms of thearticles; and in that event, one of the lateral sealing units may beomitted. The means for trimming the film along each edge, as shown inthe drawings, is optional and may be omitted. Other modifications in theequipment and process will suggest themselves to persons skilled in theart.

What I claim is:

1. Packaging equipment which comprises two sources of stretched film,cut-off equipment, a conveyer for moving articles toward the cut-offequipment, and means for holding the films together on opposite sides ofthe articles while on the conveying means and outside of this, heatedmeans equipped with means for bringing it into contact with the lm. y

2. Packaging equipment which comprises a conveyer for carrying articlesto be packaged to cut-off means, toward each edge of the conveyer a beltarranged parallel with the conveyer, means for pressing the belts towardthe conveyer, and

heated means located outside the belts and means for pressing the sameonto the belts.

3. The method of packaging articles between two pieces of thermallyshrinkable, stretched, heat-scalable lm which comprises enclosingsuccessive articles in a substantially straight line between the twofilms by pressing the two lms together along the sides of the articles,and then while thus holding the films together so as to prevent theirshrinking toward the articles, heating them outside the holding means soas to unite them.

4. The method of packaging articles between two pieces of thermallyshrinkable, stretched, heat-scalable film which comprises enclosingsuccessive articles in a substantially straight line between the twofilms by pressing the two films together along the sides of thearticles, and then while thus holding the films together so as toprevent their shrinking toward the articles, heating them outside theholding means so as to unite them, and then grasping the sealed filmsbetween each two articles by separated transverse means, and thenheating the lms between these means to cut through them and uniting thelrns by heat on each side of the cut-off effected in this manner.

5. The method of packaging articles which comprises enclosing articlesin stretched nlm, moving the film toward cut-off means, pressingportions of the film near the respective edges of said portions togetherwhile the lm is so moving and also, while the film is so moving, heatingthe film between said edges and the place where the film is pressedtogether.

HAROLD J UDSON OSTERHOF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED vSTATES PATENTS Number Name Date 1,724,208 Lewis Aug. 13, 19292,027,232 Hutt et al Jan. 7, 1936 2,142,505 Gammeter Jan. 3, 19392,195,583 Schultz et al Apr. 2, 1940 2,232,783 Hausheer Feb. 25, 19412,237,119 Smith Aplr. 1, 1941 2,257,823 Stokes Oct. 7, 1941 A 2,322,298Johnston June 22, 1943 2,380,914 Billeb Aug. 7, 1945 2,390,550 MooreDec. 11, 1945

